. 


i 


<*M  ; V r*^-: 


* -w 


I 


THE  TERNARY  SYSTEM  : BENZENE,  ACETIC  ACID, 

AND  WATER 


BY  A.  T.  LINCOLN 

It  was  shown  by  Bancroft,1  about  ten  years  ago,  that  the 
condition  of  equilibrium  in  a large  number  of  cases  of  physical 
reactions  could  be  represented  by  the  Law  of  Mass  Action ; that 
the  exponential  factors  are  not  necessarily  integers  and  in  most 
cases  are  not ; and  that,  as  in  the  case  of  chemical  reactions, 
they  are  independent  of  the  temperature.  He  showed  that  in 
the  case  of  two  non-miscible  liquids  and  a consolute  liquid,  the 
equilibria  can  be  represented  by  the  Mass  Caw  Equation,  and 
that  there  are  only  two  sets  of  equilibria  over  the  whole  range 
of  concentration,  and  these  are  represented  by  two  different 
equations.  He  has  shown  the  application  of  the  mass  law  to  a 
large  number  of  other  cases  of  physical  reactions,  such  as,  to 
two  partially  miscible  liquids  and  a consolute  liquid,  to  the  pre- 
cipitation of  a salt  by  a liquid,  to  the  precipitation  of  a liquid 
by  a salt,  and  to  the  precipitation  of  one  salt  by  another.  In 
none  of  these  latter  cases,  however,  has  the  relation  between  the 
facts  and  theory  been  worked  out  as  yet  with  a very  high  degree 
of  accuracy. 

In  the  case  of  one  ternary  system,  benzene,  water,  and  alco- 
hol, the  writer2  has  shown  that  the  Mass  Caw  Equation  does 
represent  the  conditions  of  equilibria  with  a very  high  de- 
gree of  accuracy,  and  that  the  Caw  of  Mass  Action  is  applicable 
to  this  physical  reaction,  also,  that  the  exponential  factors  are 
independent  of  the  temperature  as  in  the  case  of  chemical  re- 
actions. Previously,  Waddell3  studied  the  system,  benzene, 
acetic  acid,  and  water.  He  concludes  from  his  experiments, 
that  the  Caw  of  Mass  Action  does  not  apply  to  this  physical  re- 
action, that  the  equilibria  are  not  represented  by  simple  expo- 


1 Proc.  Am.  Acad.  30,  324  (1894). 

2 Jour.  Phys.  Chem.  4,  161  (1900). 

3 Ibid.,  3,  233  (1898). 


249 


' 


7>  i\ 


Benzene , Acetic  Acid  and  Water 

nential  formulae,  and  that  at  higher  temperatures  the  deviation 
from  the  Mass  Law  Equation  is  very  much  more  pronounced 
than  at  lower  temperatures.  In  view  of  the  fact  that  my  work 
had  shown  such  a marked  approximation  of  the  experimental 
results  to  the  values  required  by  the  theory  in  the  case  of  a sys- 
tem analogous  to  this  one  with  which  Waddell  worked,  it  seemed 
worth  while  to  repeat  his  work  and  to  ascertain  if  his  conclu- 
sions are  correct.  With  this  in  view  the  work  was  undertaken, 
and  the  results  are  given  below. 

The  thiophene-free  benzene  employed  was  fractionated  and 
that  portion  coming  over  at  79.50  C under  a pressure  of  755.8  mm 
was  collected  and  then  recrystallized  twice.  The  distilled  water 
of  the  laboratory  was  treated  with  barium  hydroxide  in  contact 
with  which  it  remained  for  several  days,  when  it  was  siphoned 
off  and  distilled.  This  distillate  was  collected  by  means  of  a 
block  tin  condenser  and  only  the  middle  portion  of  the  distillate 
was  collected.  A sample  of  the  acetic  acid  was  fractionated  a 
number  of  times  and  the  portion  coming  over  between  1150- 
11 6. 50  was  collected  and  recrystallized  many  times.  This  sam- 
ple had  a melting-point  of  14.6°,  and  according  to  Allen,1  repre- 
sents a purity  of  98.7  percent.  On  titration  with  a N/40  barium 
hydroxide  solution  it  was  found  to  be  98.6  percent  pure.  In  all 
the  following  work  a correction  was  made  for  the  water  con- 
tained in  acetic  acid  of  this  purity. 

All  of  the  flasks  and  bottles  used  were  thoroughly  cleaned 
and  steamed.  The  bottles  in  which  the  benzene,  water  and 
acetic  acid,  as  well  as  the  standard  solution  of  barium  hydroxide, 
were  stored,  were  connected  with  accurately  calibrated  burettes, 
which  were  so  arranged  that  the  air  which  entered  the  bottles 
passed  through  drying  vessels  containing  sulphuric  acid  or 
potassium  hydroxide.  They  were,  also,  so  connected  that  when 
the  burettes  were  emptied,  the  air  which  took  the  place  of  the 
liquid  came  from  the  storage  bottles.  By  these  precautions  the 
solutions  were  thoroughly  protected  during  the  series  of  experi- 
ments. 

1 Commercial  Organic  Analysis,  I,  p.  387. 


,13840 


250 


A.  T Lincoln 


The  determinations  were  made  in  50  cc  flasks  (or  in-  200  cc 
flasks)  which  had  been  thoroughly  cleaned  and  steamed.  Into 
one  of  the  flasks  were  introduced  5 cc  of  acetic  acid  (or  100  cc) 
and  to  this  was  added  a definite  quantity  of  benzene,  and  then 
enough  water  was  introduced  to  produce  clouding  at  room  tem- 
perature. The  mixture  was  then  warmed  up  a few  degrees 
above  the  temperature  at  which  the  determination  was  to  be 
made.  When  the  contents  of  the  flask  became  homogeneous  the 
flask  was  transferred  to  a bath  which  was  kept  at  the  desired 
temperature.  After  remaining  in  the  bath  long  enough  to  ac- 
quire the  temperature  of  the  same,  if  clouding  did  not  result, 
the  flask  was  removed,  and  a few  drops  of  water  added  from  the 
burette,  and  the  flask  warmed  until  the  contents  became  homo- 
geneous, when  it  was  returned  to  the  bath  and  allowed  to  remain 
with  occasional  shaking  until  it  had  acquired  the  temperature  of 
the  bath.  If  clouding  did  not  result,  this  process  was  continued 
until  it  was  found  that  one  drop  of  water  caused  the  second 
liquid  layer  to  appear.  In  order  to.  ascertain  this  point  the  flask 
had  to  be  removed  from  the  bath  in  which  it  was  kept.  So  in 
order  to  make  the  observation  and  at  the  same  time  prevent  the 
clouding  resulting  from  cooling  the  walls  of  the  flasks  by  con- 
tact with  the  air,  the  flasks  were  placed  in  a beaker  in  the  bath 
and  the  beaker  containing  the  flask  and  water  from  the  bath  was 
removed  and  the  observation  made. 

The  bath  employed  was  an  ordinary  Ostwald  thermostat 
provided  with  a water  turbine  for  stirring  and  no  difficulty  was 
experienced  in  keeping  the  temperature  constant  to  within  a few 
hundredths  of  a degree. 

In  the  manner  just  described  the  data  given  in  the  follow- 
ing tables  were  collected.  In  Table  I are  the  data  for  the  equilib- 
rium determinations  at  25 0 C and  the  calculated  values  for  the 
amount  of  water  that  should  have  been  found  and  also  the 
values  of  the  constant  are  given  in  the  last  column.  The  head- 
ings of  the  other  columns  are  self-explanatory. 

In  Table  II  are  given  the  data  for  the  determinations  made 
at  350  C.  The  headings  of  the  columns  are  self-explanatory 


Benzene , Acetic  Acid  and  Water  251 

except  the  column  marked  3,  which  contains  the  values  found 
in  order  to  produce  the  same  degree  of  clouding.  We  shall  refer 
to  this  subsequently. 

TabIvE  I. 

Temperature  25 0 

x — cc  benzene,  y = cc  water  per  5 cc  acetic  acid 


Formula  n log  x -|-  log  y = log  C 
Tog  0 = 0.2875;  # =0.6136 


x benzene 

y water 

log  C 

Found 

Calculated 

I 

10.06 

0-45 

0-445 

0.2829 

10.06 

o-45 

0.445 

0.2829 

2 

8.04 

0.57 

0.54 

0.31 14 

8.04 

o.55 

0.54 

0.2959 

8.04 

o.55 

0.54 

0.2959 

3 

6.03 

0.64 

0.64 

0.2850 

6.03 

0.62 

0.64 

0.2710 

4 

5-03 

0.72 

0.72 

0.2878 

5.03 

0.69 

0.72 

0.2694 

5.03 

0.70 

0.72 

0.2756 

5 

3.02 

0.99 

0.98 

0.2903 

3.02 

0.97 

0.98 

0.2814 

6 

2.51 

1. 12 

1. 10 

0.2947 

2.51 

1. 12 

1. 10 

0.2947 

7 

2.01 

I.29 

1.26 

0.2966 

2.01 

I.27 

1.26 

0.2898 

8 

I*5I 

1.47 

1.50 

0.2771 

1. 5i 

1.49 

1.50 

0.2830 

9 

1. 01 

i-93 

i-93 

0.2882 

1. 01 

1.87 

i-93 

0.2745 

10 

0.80 

2.23 

2.22 

0.2889 

0.80 

2.20 

2.22 

0.2830 

252 


A.  T.  Lincoln 


Table  I.  — ( Continued ). 

Formula  n!  log  x -f-  log_y  = log  C'  = 0.244  ; n — 0.9166 


x found 

y found 

x calc. 

y calc. 

log  cy 

1 1 

O.60 

2.81 

0.608 

2.80 

0.2438 

O.60 

2.80 

0-599 

2.80 

0.2453 

12 

0.50 

3.26 

0.510 

3-3i 

0.2373 

O.50 

3-25 

0.511 

3-3i 

0.2360 

13 

0-35 

4-55 

0.320 

4-59 

0.2401 

0-35 

4-53 

0.321 

4-59 

0.2382 

H 

O.23 

6.82 

0.228 

6.75 

0.2487 

0.22 

6.82 

7.00 

0.2310 

15 

0.17 

9-53 

0.158 

8.91 

0.2738 

0.16 

9-53 

9.42 

0.2496 

One  of  the  greatest  difficulties  to  be  contended  with  in  the 
experimental  work  was  obtaining  the  point  of  equilibrium.  It 
was  difficult  to  detect  the  appearance  of  the  second  liquid  layer 
as  it  did  not  manifest  itself  in  the  same  manner  over  the  whole 
range  of  concentration.  Over  one  portion  there  was  first  a very 
slight  opalescence  which,  upon  further  addition  of  water,  in- 
creased until  a decided  cloudiness  resulted,  and  finally  the  second 
liquid  layer  was  very  apparent.  Over  the  other  portion  of  the 
concentrations  where  the  water  was  in  excess  of  the  benzene,  the 
second  liquid  layer  appeared  as  fine  clear  globules  which  floated 
on  the  surface,  thus  indicating  that  it  was  the  benzene  layer 
that  was  separating  out.  Owing  to  these  two  different  appear- 
ances of  the  second  liquid  layer,  it  was  somewhat  difficult  to 
determine  the  true  point  of  equilibrium. 

It  was  no  doubt  this  difficulty  which  presented  itself  to 
Waddell  when  he  determined  the  equilibrium  of  the  system  ben- 
zene, acetic  acid  and  water,  for  he  states  that  he  took  as  the  end- 
point, i.  e.,  as  the  point  of  equilibrium,  the  same  degree  of  cloud- 
ing. That  one  cannot  use  the  same  degree  of  clouding  as  the 
end-point  for  the  establishment  of  equilibrium  is  very  apparent 


Benzene , Acetic  Acid  and  Water 


253 


Table  II. 

Temperature  35 0 C 

x = cc  benzene,  y = cc  water,  per  100  cc  acetic  acid 
Formula  n log  x -f-  log y — log  C = Mean  = 0.810.  n = 0.610 


(1) 

x found 

(2) 

y found 

(3) 

y calc. 

log  C 

18.  IO 

1. 16 



I.  II 

0.8322 

18.  IO 

1. 12 

— 

1. 11 

0.8169 

2 

16.09 

1.22 

1.26 

1.23 

0.8061 

16.09 

I. 21 

1.26 

1.23 

0.8025 

3 

10.06 

I.56 

1.79 

1.58 

0.8051 

IO.06 

i*54 

1. 81 

1.58 

o-7995 

4 

6.03 

2.18 

2.30 

2.  l6 

0.8148 

6.03 

2.17 

2.30 

2.  l6 

0.8128 

5 

4.02 

2.77 

— 

2.76 

0.8113 

4.02 

2.78 

— 

2.76 

0.8129 

6 

3.OI 

3-27 

— 

3-30 

b.8067 

3.OI 

3-25 

— 

3*30 

0. 8040 

Formula  n'  log  x — log y — log  C'  = Mean  = 0.842. 

n = 0.92 

x calc. 

y calc. 

log  C' 

7 

I. OO 

7.01 

1. 01 

6.95 

0.8457 

I. OO 

7.00 

I. Ol 

6-95 

0.8451 

8 

0.65 

10. 10 

0.666 

10.33 

0.8322 

0.66 

10. 10 

0.666 

10. 19 

0.8383 

9 

0.48 

13.64 

0.480 

13-65 

0.8416 

0.47 

13.64 

0.480 

13.92 

0.8331 

from  the  fact  that  in  one  portion  of  the  series  of  concentrations 
there  is  a decided  clouding,  while  at  the  other  end  of  the  series 
there  is  no  clouding,  but  the  separation  of  the  second  liquid 
layer  as  clear  transparent  globules.  In  that  portion  of  the  con- 
centrations where  decided  clouding  does  take  place,  the  same  de- 


254 


A.  T.  Lincoln 


gree  of  clouding  does  not  represent  the  points  of  equilibrium. 
For  example,  in  one  experiment,  No.  3 at  30°,  it  requires  1.56 
cc  of  water  to  produce  a decided  opalescence  and  1.79  cc  to  pro- 
duce a decided  clouding,  while  in  another  experiment  opales- 
cence was  produced  by  the  addition  of  2.18  cc,  while  the  same 
degree  of  clouding  as  in  the  preceding  experiment  was  produced 
by  2.30  cc  of  water.  The  calculated  value  in  the  first  case  was 
1.58  cc  and  in  the  second  2.16  ccof  water.  In  Table  II,  column 
3,  are  the  values  of  the  quantities  of  water  that  were  required 
to  produce  the  same  degree  of  clouding  in  these  various  cases. 
By  comparison  with  the  corresponding  values  in  column  2 it 
will  be  observed  how  much  more  was  required  than  that  just 
necessary  to  produce  the  decided  opalescence  which  we  took  as 
the  indication  of  the  appearance  of  the  second  liquid  layer,  that 
is,  as  the  point  of  equilibrium.  From  this  I think  we  are  justi- 
fied in  concluding  that  Waddell’s  results  are  wrong.  He  was  not 
working  with  a system  in  equilibrium,  but  had  an  excess  of 
one  of  the  components,  and  for  that  reason  we  could  not  expect 
the  results  to  conform  to  the  law  of  Mass  Action. 

If  we  apply  the  law  of  Mass  Action  to  the  data  given  in 
the  tables  above  wherein  we  let  x = cc  of  benzene,  y — cc  of 
water,  and  2 = cc  of  acetic  acid,  then  our  equation  takes  the 
form  xayp  — 2a  + p.  Since  the  acetic  acid  was  kept  constant  and 
we  have  xayp  = C1,  and  if  we  define  a//3  = n , our  equation  then 
takes  the  form  xny  — C,  or  expressed  logarithmically,  we  have 
n log  x + log  y = log  C.  Now  this  is  in  the  form  of  the  equa- 
tion of  a straight  line  wherein  we  have  the  logarithm  of  the 
quantities  in  place  of  the  quantities  themselves.  Hence,  if  we 
plot  the  logarithm  of  the  quantities  of  benzene  and  water  used, 
the  resulting  curve  should  be  a straight  line  with  the  slope  n. 
From  this  curve  the  value  of  n can  be  determined,  which  in  the 
case  of  the  determinations  at  250  C given  in  Table  I are  plotted 
on  Fig.  1.  It  will  be  readily  seen  that  we  have  two  distinct 
curves  and  that  one  curve  does  not  represent  the  condition  of 
equilibrium  over  the  whole  range  of  concentration  ; but  confirms 
Bancroft’s  statements  that  for  two  non-miscible  liquids  and  a 
consolute  liquid  there  are  two  sets  of  equilibria,  and  we  have 


Benzene , Acetic  Acid  and  Water 


255 


two  curves  corresponding  to  these  two  sets  of  equilibria.  Fur- 
ther, the  different  end-points  seem  to  correspond  with  these  two 
sets,  for  over  the  greater  part  of  one  we  get  the  second  liquid 
layer  appearing  as  fine  transparent  globules  and  over  a consider- 
able part  of  the  other  as  an  opalescence.  Having  determined  the 
values  for  n and  n\  we  then  have  the  distinct  curves  of  dif- 
ferent slopes.  If  now  we  substitute  the  value  of  n and  n ' in 
their  respective  equations  we  obtain  the  values  for  log  C and 
log  C1  as  given  in  the  last  column.  If  the  mean  value  be  substi- 
tuted in  our  formula  and  we  solve  for  the  value  of  the  amount 
of  water  that  should  have  been  added,  we  obtain  the  values 
given  in  column y calc , which  agrees  fairly  well  with  those  found 
experimentally  and  given  in  column  2.  Under  x calc  are  given 
the  calculated  values  for  benzene,  assuming  the  value  of  y 
known. 


93  iao  10.3  1 1.0 


Fig.  1 

If  this  physical  reaction  follows  the  Mass  Law  the  expo- 
nential factors  should  be  independent  of  the  temperature,  i.  e., 
the  values  of  n should  be  the  same  at  whatever  temperatures 
the  equilibrium  is  established.  Waddell  states  that  at  35 0 C the 
deviation  of  this  equilibrium  from  the  Mass  Law  is  even  more 


256  Benzene , Acetic  Acid  and  Water 

pronounced  than  at  250  C.  A series  of  determinations  was  made 
at  350  C and  the  results  are  given  in  Table  II,  and  the  plotted 
results  are  represented  in  Fig.  1.  It  will  be  observed  that 
there  are  two  curves  corresponding  to  the  two  equilibria  and 
further  the  value  of  n (0.61)  at  350  is  very  nearly  the  same  as  n 
(0.6136)  at  250,  while  the  values  for  n’  (0.92  against  0.9166)  are 
almost  exactly  the  .same  at  both  temperatures.  Hence  it  seems 
that  we  are  justified  in  concluding  that  the  temperature  does 
not  affect  the  value  of  the  exponential  factor  and  that  this 
physical  reaction  between  benzene,  acetic  acid  and  water  con- 
forms to  the  Mass  Law  Equation. 

In  this  paper  we  have  shown  : 

1.  That  Waddell  was  wrong  in  selecting  the  same  degree 
of  clouding  as  the  point  of  equilibrium  in  the  system  benzene, 
acetic  acid  and  water. 

2.  That  equilibrium  in  the  system  benzene,  acetic  acid  and 
water  can  be  represented  by  the  Mass  Law  Equation. 

3.  That  for  the  range  of  temperature  from  250  to  350  the 
exponential  factor  is  constant,  as  in  the  case  of  chemical  reac- 
tions. 

I wish  to  express  my  gratitude  to  Mr.  J.  V.  Mapes,  who  did 
a part  of  the  experimental  work  herein  presented. 

University  of  Illinois , 

Feb.,  1904. 


